1. Field of the Invention
The present invention relates to a hydrogen generation apparatus of generating a reformed gas by reforming a fuel such as a hydrocarbon-based fuel and to a fuel cell system or the like using the hydrogen generation apparatus.
2. Related Art of the Invention
Because a fuel-cell power-generating system using a fuel cell has a high power-generation efficiency and moreover, the heat produced with power generation can be effectively used, application of the system to household cogeneration is expected.
In the case of a household purpose, it is preferable to operate a fuel-cell power-generating system at a comparatively low temperature from the viewpoints of correspondence to frequent start/stop of an apparatus, durability of the apparatus, and cost cutting. Therefore, development of a polymer electric fuel cell using a polymer electrolytic film as a power-generating section is progressed.
Most fuel cells generate power by using hydrogen as a fuel. However, because a reformed-gas infrastructure is not prepared at present, a power-generating system uses not only a fuel cell but also a hydrogen generation apparatus provided with a reformer of generating a reformed gas containing hydrogen by making a hydrocarbon component such as natural gas or LPG, alcohol such as methanol, or a material such as a naphtha component react with water.
Not only hydrogen but also carbon dioxide and carbon monoxide are contained in the reformed gas generated by the reformer as auxiliary components. Because a polymer electric fuel cell being currently developed operates at a low temperature of 100° C. or lower, it is necessary to minimize the carbon monoxide contained in a reformed gas in order to maintain the activity of a cell electrode catalyst. Therefore, a hydrogen generation apparatus has a configuration of using not only a reformer of generating a reformed gas but also a carbon-monoxide-removing section constituted by a shifter of making carbon monoxide shift-react with water and a purifying section of oxidizing carbon monoxide.
The efficiency of the hydrogen generation apparatus is further deteriorated as the heat quantity to heat the reformer up to a temperature necessary for a reforming reaction increases.
The hydrogen generation apparatus makes a material such as hydrocarbon react with vaporized water. However, because water has an extremely-large amount of evaporative latent heat, the reformer requires much heat in order to vaporized water. Therefore, it is difficult to raise the efficiency of the hydrogen generation apparatus up to a certain value or more.
On the other hand, because the shift reaction is an exothermic equilibrium reaction, the shifter of performing a shift reaction located at the downstream side of the reformer more easily reduces carbon monoxide as the ratio of water vapor to a reformed gas increases at a low temperature and the quantity of air to be supplied necessary for a reaction can be decreased in the purifying section at the downstream side of the shifter. Therefore, excessive consumption of hydrogen can be controlled and stable operations can be performed. By increasing the quantity of water vapor and raising a temperature, it is possible to further downsize the shifter by decreasing a catalyst volume because the shift reaction rate increases.
However, because the water vapor in the shifter is obtained by the reformer and a large amount of evaporative latent heat is necessary in order to increase the quantity of water vapor as described above, the heat quantity required to heat the reformer increases and increasing the quantity of water vapor in the reformer in order to improve the efficiency of the shifter and downsize the section causes the efficiency of the reformer to lower.
To prevent the above mentioned, a technique is proposed which performs humidification by adding separately-prepared water to a material gas (for example, refer to Japanese Patent Laid-Open No. 10-330101 and Japanese Patent Laid-Open No. 11-106204). Thereby, because evaporative latent heat to change water to water vapor is decreased, it is possible to reduce the heat quantity necessary for a reforming device and improve the efficiency of a shift reaction in the shifter. Moreover, by using the carbon-monoxide-removing section or the heat of the cooling water for a fuel cell, it is possible to perform humidification without lowering the efficiency.
However, a material gas used for a conventional hydrogen generation apparatus is only humidified by using a heat source in the generator. Thereby, problems occur that improvement of efficiency is limited and piping for heat recovery and humidification becomes complicated.